Angular dependent magnetothermopower of α-(ET)₂KHg(SCN)₄

The magnetic field and angular dependences of the thermopower and Nernst effect of the quasi-twodimensional (q2D) organic conductor α-(ET)₂KHg(SCN)₄ are experimentally measured at temperatures below (4 K) and above (9 K) the transition temperature to fields of 31 T. In addition, a theoretical model which involves a magnetic breakdown effect between the q1D and q2D bands is proposed in order to simulate the data. Analysis of the background components of the thermopower and Nernst effect imply that at low temperatures, in the CDW state, the properties of α-(ET)₂KHg(SCN)₄ are determined mostly by the orbits on the new open Fermi sheets. Quantum oscillations observed in the both thermoelectric effects, at fields above 8 T, originate only from the α orbit

Angular dependent magnetothermopower of alpha-(ET)2KHg(SCN)4

The magnetic field and angular dependencies of the thermopower and Nernst effect of the quasi-two-dimensional organic conductor alpha-(ET)2KHg(SCN)4 are experimentally measured at temperatures below (4 K) and above (9 K) the transition temperature to fields of In addition, a theoretical model which involves a magnetic breakdown effect between the q1D and q2D bands is proposed in order to simulate the data. Analysis of the background components of the thermopower and Nernst effect imply that at low temperatures, in the CDW state, the properties of alpha-(ET)2KHg(SCN)4 are determined mostly by the orbits on the new open Fermi sheets. Quantum oscillations observed in the both thermoelectric effects, at fields above 8 T, originate only from the alpha orbit.Comment: 25 pages, 18 figure

Thermoelectric mechanism of electromagnetic-acoustic transformation in organic conductors

The thermoelectric mechanism of electromagnetic-acoustic transformation of the energy in an organic conductor with a quasi–two-dimensional electron energy spectrum (Q2D) placed in an external magnetic field has been considered. The amplitude of the acoustic wave excited by the temperature oscillations in a Q2D organic conductor was calculated for both the isothermal and the adiabatic thermal boundary condition. Angular oscillations of the amplitude resulting from the periodic dependence of the electron velocity on the angle between the normal to the layers and the magnetic field has been observed as expected. A comparison with the inductive mechanism of EMAT is made in order to determine the conditions at which the thermoelectric mechanism is dominant over the inductive one in the presence of a magnetic field. The thermoelectric mechanism of EMAT allows new important information on the electronic structure of the organic layered conductors to be obtained

Non-contact ultrasonic measurements of the elastic constants of magnetic materials

Ultrasonic testing using contacting transducers such as quartz or PZT is well established. However, standard measurement techniques used require physical contact of the sample and ultrasonic transducer and some sort of couplant between the two. With this configuration there is a possibility of damaging the sample, transducer or bond during testing, thermal cycling, or removal of the transducer. We present results taken using recent advances in non-contact methods of ultrasound generation and detection using electromagnetic acoustic transducers (EMATs), which offer some significant benefits over contact ultrasonic techniques. Circumventing the need for couplant removes the possibility of contaminating the system, which is an issue for some material property measurements, and allows easier measurements over a wider range of temperatures. An automated data analysis system has been developed which allows the velocity of sound in the sample, and hence the elastic constants, to be determined to a high accuracy. This technique is illustrated using measurements of the alloy Gd(64)Sc(36)

High frequency properties of a quasi-two-dimensional conductive film

The propagation of a monochromatic longitudinal acoustic wave along the low conductivity axis of a thin quasi-two-dimensional conductive film, in the absence of an external magnetic field, is studied theoretically. It is shown that under certain conditions the formation of both a standing ordinary wave (OAW) and an anomalous acoustic wave (AAW) is possible. The frequency dependence of the amplitudes of both waves is derived. For certain values of the characteristic parameters, the AAW in the film may be dominant. From the resonance conditions for the formation of standing OAW and AAW waves (especially the AAW), it is possible to obtain information about the electronic structure of the quasi-two-dimensional conductors, e.g. the corrugation parameter η or the relaxation properties of the charge carriers. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005